To improve the quality of wireless communication, there is a demand for a wireless device that outputs only desired signals and does not output unwanted signals. Examples of unwanted signals include a leak (local leak) of a local signal (carrier signal). In the wireless device, the local signal drives a mixer, and a high power level is required to drive the mixer. Therefore, suppression of the local leak is a major issue, and various techniques for dealing with this issue are publicly known.
In this regard, Patent Literature 1 discloses a local leak reduction circuit for reducing local leaks. The local leak reduction circuit supplies a test signal to a quadrature modulation unit within the local leak reduction circuit. A baseband signal having an amplitude of 0 is used as the test signal. The use of such a test signal allows the signal output from the quadrature modulation unit to include only local signal components that are input to the quadrature modulation unit. Accordingly, the signal output from the quadrature modulation unit is treated as the local leak. In this case, a level detection unit detects the level (power) of the local leak and adds an offset to the baseband signal so as to minimize the detected power. This results in reducing the local leak.
Patent Literature 2 also discloses a technique in which a signal for test is input to detect power output from the quadrature modulation unit, and the input signal is controlled based on the detected result.
In recent years, wireless devices using a beam forming technique have been actively developed to improve the communication quality and to provide over-the-horizon communication. In a typical transmission device using the beam forming technique, a single baseband signal is input to a transmitting circuit and high-frequency signals are output from a plurality of antennas. There is an appropriate phase difference between the output high-frequency signals, so a desired beam pattern is obtained. The transmission device using the beam forming technique includes a plurality of high-frequency circuits, and a single baseband signal is converted into a plurality of high-frequency signals.